When lumber is sawed into pieces or fabricated into a specified shape in a wood mill, a great amount of wood debris and wood dust is generated. The floating wood debris and wood dust will contaminate the air and harm the health of the workers. Therefore, wood mills generally have large-size dust collectors. Refer to FIG. 1 for a conventional dust collector. The upper side of the conventional dust collector has a motor 1 with a fan (not shown in the drawing) therebelow. The conventional dust collector has an air inlet pipe 2. When the motor 1 drives the fan to rotate, external air is sucked to enter the air inlet pipe 2 and pass through an inner filter. Thus, wood debris and wood dust is filtered out by the filter. The conventional dust collector has a dust tank 3 at the lower-left side thereof. A plastic bag 4 is arranged inside the dust tank 3 to receive wood debris and wood dust. The air having passed through the filter is guided to a filter tank 5 at the right side and then goes out from the dust collecting bag 6 below the filter tank 5, wherein the dust collecting bag 6 can filter out smaller particles.
The motor 1 drives the fan to rotate and generates an intense suction force, which sucks external air into the conventional dust collector. However, the suction force also sucks the plastic bag 4 and makes the plastic bag 4 hard to expand. Therefore, there should be a brace to support the plastic bag 4. However, the suction force will still draw up the plastic bag 4 and thus tear holes on the plastic bag 4.